Thursday, December 11, 2008
Algol Blinks


Algol is one of the classic variable stars, unlike the red giant Mira which changes brightness through its expansion and contraction, Algol is an eclipsing binary. The bright star has a dimmer companion which passes in front of it just short of every three days causing the star to appear to "blink" (if dimming over 5 hours is a blink). No wonder the stars name means ‘Blinking Demon”.
Algol is very difficult to see from the southern hemisphere, it is below the horizon for a good chunk of the year, and even when it is visible, it is very low to the horizon. This means the times to observe Algol dim are few from the southern hemisphere. However, in the next week there are two good opportunities to see Algol "blink", on the 14th (13th in WA) and 16th of December.

The next minima is on the 16th at 10:44 UT which is 7: 44 pm AWDST in WA, before sunset. So WA folks miss out. However, in Central and Eastern states it is 9:14 pm ACDST (after civil twilight) and 9:44 pm AEDST (astronomical twilight). The charts for this are at the top of the page. At this time you will miss the dimming, but can easily watch Algol return to brightness.
The total "blink" time (from start of dimming to minimum brightness then back to full brightness) is 10 hours, but you can easily see Algol rapidly change in brightness over an hour or so. At minimum, Algol is as bright as the dim star immediatley above it. You can use the magnitudes shown in the finder chart above to keep track of Algols dimming or rise as outlined in the post about Mira.
So when you are out and about, keep and eye on Algol and you may see it blink!
Labels: variable star